In the natural environment lignocellulosic materials in the form of forest litter and the like are rapidly broken down by mineralization and carbon cycling processes mediated by a host of insects and microorganisms. Many timber and wood-containing products, particularly those from softwood species, are also subject to insect damage as well as fungal degradation and discolouration. The most problematic insects are termites, ants, boring insects, weevils and various beetles. Timber and wood products may be protected against wood degrading organisms by the application of insecticides and fungicides.
Traditional methods of timber protection involve aqueous impregnation with inorganic preservatives such as copper chrome arsenic, sodium octaborate, alkaline copper quat (“ACQ”) using vacuum and pressure, or the use of carbon-based preservatives in a solvent delivery system such as a light organic solvent preservative (“LOSP”). Both approaches produce high levels of active ingredient penetration but are expensive. Additionally the former method requires special care to avoid problems with dimensional stability and the latter method leaves solvent residues. Simpler and cheaper treatment options, generally suitable for lower hazard product applications such as enclosed building materials, include delivery of preservatives in the glues and resins used to make engineered wood products such as plywood and laminated veneer lumber and reconstituted wood products such as medium density fibreboard and the like. In the case of sawn timber or dimensional lumber, as well as wood products, surface treatment operations such as surface spraying or brief dipping procedures provide adequate protection, particularly against insect pests.
Most surface treatment operations are carried out in a sawmill or a wood processing mill and occur after the timber or wood product has been gauged, trimmed and cut to final dimensions, sanded etc. Post-treatment operations such as sawing, drilling etc, occur mainly on building sites or in a factory such as a frame and truss manufacturing facility where timber is sawn to produce framework such as trusses and other preassembled structures. These post-treatment operations expose new surfaces that have not been treated directly with insecticide. Accordingly, with surface-treated timber or wood products, it is industry practice to provide a secondary treatment operation in which the newly exposed surfaces are treated with insecticide before the structural members are nailed or otherwise fixed into place but this involves additional time, expense and risk to workers.
New generation insecticides including certain members of the neonicotinoid class of insecticides (for example imidacloprid, thiacloprid, dinotefuran, clothianidin and nitenpyram), phenylpyrazoles (for example fipronil and ethiprole), anthranilic diamide insecticides (for example rynaxypyr and flubendiamide), spinosyns (for example spinosad and spinetoram), chlorfenapyr and indoxacarb are not considered to have repellent activity toward insects that damage timber and wood products such as termites, ants, boring insects and the like.
These non-repellent insecticides are now the active ingredients of choice for eradication of collections of problematic ground-dwelling insects such as termite or ant colonies, because foraging members of the colony that encounter the insecticide (within an appropriate bait) are not repelled and instead are able to consume the insecticide, carry it back to the colony and spread the insecticide among other members of the colony before they die.
The prior art teaches that non-repellent insecticides used as a surface treatment for timber or wood products are unable to prevent insect damage to any untreated surfaces and that to avoid the need for secondary insecticide treatment of newly cut surfaces, for example on a building site, it is necessary to use surface treatment compositions and methods that utilise repellent insecticidal active ingredients. These compositions are both lethal to the target insects and repellent with respect to the target insects. This is based on prior art observations that untreated wood surfaces exposed after the initial surface treatment operation, for example the ends of sawn timber, provide a point of entry for insects unless an insecticide with repellent activity is present on neighbouring treated surfaces. Insecticides with repellent activity that may be used in surface treatments include synthetic pyrethroids such as permethrin, deltamethrin, cypermethrin and bifenthrin. Unfortunately these active ingredients have relatively high mammalian toxicities and workers handling products containing these active ingredients commonly experience paresthesia or skin irritation to varying extents.